Sheet molding compounds are made commercially by utilizing polyester resin forming material of a type which utilize one type of chemical reaction to convert the resin prepolymer from a sticky paste into a semi solid, and which utilize another type of chemical reaction to convert the polyester resin into an insoluble infusible state. In the case of polyesters, the second reaction is accomplished by the crosslinking of unsaturate bonds using an unsaturated liquid monomer; and the first chemical reaction is accomplished by reacting the carboxyl end stopped prepolymer molecules with an alkaline material such as calcium or magnesium oxide. The liquid monomer that is necessary for the second stage of reaction must be present during the first stage reaction, and this liquid monomer works against the conversion of the materials to a solid handleable state during the first stage reaction. Therefore, the prior art sheet molding compound must be made between impervious sheets while in the unhandleable state and must be cured for several days in maturation rooms in order to achieve the handleable state and must be prevented from becoming dried out so that it does not lose its reactive liquid monomers.
A principal object of the present invention is the provision of a new and improved method of making sheet molding compound which does not require organic liquids to be present, and which does not need to be prevented from drying out.
Another object of the present invention is the provision of a new and improved process for making sheet molding compounds wherein the first and second stages of curing involves formation of methylol groups and/or the removal of water.
A further object is the production of sheet molding compounds from aldehyde condensates.